SDR and cognitive radio: the new horizons of military communications

Software-defined radio is opening up a whole new way for warfighters to send and receive voice, data, and imagery in Internet-like fashion, and is pointing the way to a new generation of combat radios that could be considered tactical cell phones.

BY John Keller

Previous generations of soldiers who struggled with interference-laden combat radios, which offered no guarantees of getting important messages through, might be amazed at what modern military radios offer to the warfighter.

General Dynamics AN/PRC-154 Rifleman Radios enable soldiers on the battlefield to have secure, mobile voice, video, and data communications capabilities that are similar to those available through commercial cellular networks. (Photo courtesy JPEO JTRS.)

Military radio communications has progressed light years beyond those crackly sounding, two-handed walkie- talkies that we see in old movies. Military wireless communications on the battlefield today increasingly consists of software-defined radio (SDR), which not only can adapt to a wide variety of communications protocols to enhance interoperability among different military services and allied forces, as well as among military and civil authorities, but also could be the basis of a future wireless tactical Internet for the battlefield designed to connect computers and provide cell phone-like connectivity.

The latest military radio communications go far beyond simple voice and data. Modern combat radios are starting to offer a variety of functions that take place in the background without the user's intervention or knowledge. Military radios today can act as communications repeaters and network-control devices to facilitate voice and data networking on the move. In the future, each radio on the battlefield might act as a secure, wireless node to provide Internet connectivity to rugged handheld devices, such as smartphones, electronic tablets, and laptop computers.

Tomorrow's combat radios will offer even a broader variety of functions that are transparent to the user. While today's radios also are repeaters and network-control devices, tomorrow's radios will be able to offer chemical, biological, and nuclear agent detection and mapping, situational awareness of where friendlies and enemies are located, data on the availability of artillery fire support, and the ability to call in air strikes faster than ever before.

Anticipated future developments in combat radios also are expected to augment software-defined radio technology with an approach experts call cognitive radio. This will offer the ability for radios to sample the surrounding environment, determine where interference and electronic warfare jamming are blocking certain frequencies, and automatically choose the best frequencies on which to communicate and set up an ad-hoc network on the fly to make best use of those clear frequencies.

What is software-defined radio?

Lots of definitions of software-defined radio exist. The consensus industry definition, according to the Wireless Innovation Forum in Phoenix, is a radio in which some or all of the physical layer functions are software-defined. If that sounds a little fuzzy, essentially SDR technology involves blending computers and radios. While legacy military radios have been designed in hardware with specific and limited functionality, SDR implements radio functionality in software, similarly to how a PC carries out word processing, Web browsing, database management, games, and other functions as computer programs that run on top of software operating systems, such as Windows and Linux.

Continuing the PC analogy, the software programs in SDR technology that determine functionality—such as frequency range, security, frequency-hop scheme, and other factors necessary to be interoperable with other radios—are called waveforms. The SDR operating system, meanwhile, which is standard for U.S. military software-defined radio systems, is called the open-systems Software Communications Architecture (SCA). SCA relies on CORBA and POSIX operating systems to coordinate different SDR waveform software modules.

"The waveform is protocol by which information will be transmitted from one place to the other, and at the other end, the information will be extracted," says Lewis Johnston, vice president of advanced programs at Thales Communications Inc. in Clarksburg, Md. "It's where the features and functions of the radio are software-reprogrammable, extending down to the radio's modulation and demodulation. Encryption is part of the waveform, so there is a whole series of steps in processing from where you speak or put data into the radio, and how it comes out the other side."

For the U.S. military, and increasingly for allied militaries throughout the world, the program driving software-defined radio development and deployment is the Joint Tactical Radio System, or JTRS. Even though some radio manufacturers may not be formally part of the JTRS program, those companies can participate in U.S. military SDR procurements, as long as their offerings comply with JTRS policies, software, and design approaches, and have testing and approval from JTRS officials.

"The key innovation in software-defined radio is that, just as you load Microsoft Word on your computer, you can load SINCGARS on your radio," explains Eric Whitehill, chief engineer at the ITT Corp. Communications and Force Protection Systems segment in Fort Wayne, Ind. ITT is among the builders of the Single-Channel Ground and Airborne Radio System (SINCGARS), a legacy military radio that ITT engineers are upgrading for SDR capability.

"The next day you decide you might need different radio properties, but would like to have some data capability," White goes on. "You could use another waveform, such as the soldier radio waveform that combines voice and data, reliability, and a nice data pipe for voice, images, video, and data. Software-defined radio is the ability to load waveforms and repurpose a hardware device to do many different functions."

Benefits of SDR

So what does software programmability bring to the table for military radio communications? The list of SDR benefits is long, but some of the most important are interoperability with new and legacy radio systems; ability to squeeze a staggering amount of radio capability in a very small package; and the ability to implement networking tasks on each radio that run transparently to the user.

"SDR lets a user program the radio for multiple frequency ranges," explains Bob Haag, vice president and general manager of communications products at Rockwell Collins in Cedar Rapids Iowa. "I can do all that in one radio now, whereas in the past, I would have needed multiple radios. SDR lets soldiers, vehicles, and aircraft come together and do their jobs better on the battlefield, such that we can move data so we know where our allies are and can get situational awareness of the battlefield."

Software-defined radio technology in the future could help enable embedded radios in other soldier-worn systems for future capabilities in situational awareness, chemical agent detection, and even electronic warfare.

Situational awareness often is touted as one of the most promising aspects of SDR, and what enables this capability is the ability of SDR to form wireless data networks on the fly. Say, for example, that each infantryman has a software-defined radio with an embedded global positioning system (GPS) sensor. That collection of radios has the capability to place the locations of each soldier on the network, and broadcast a picture to everyone in the area of where everyone is.

Perhaps a soldier's vital signs are measured and transmitted onto the network. In that way, commanders could get a quick picture of who in their units is dead, wounded, in some other kind of stress, or fully operational.

Perhaps the most important aspect of SDR technology is its ability to accept systems upgrades through software programming, which ex- pends the lifecycles of radio systems and enables users to adapt quickly to new capabilities, challenges, and threats. "We are able now to upgrade our radio products downstream and preserve the radio's lifecycle for the users. That's where we are today," says Mark Turner, engineering director of software and information assurance at the Harris Corp. RF Communications Division in Rochester, N.Y.

History of SDR

Interoperability also is a huge advantage of SDR technology, and historically has been one of the primary drivers of SDR development and deployment for military forces. "At one time, we had 200 radios in the DOD [U.S. Department of Defense] inventory, and none of them talked to each other," points out Byron Tarver technical director for the radio business of General Dynamics C4 Systems in Scottsdale, Ariz. "With the pace of battle and the need for the U.S. Army to talk to the Marines and the Air Force, it became imperative to have interoperability."

The venerable Single-Channel Ground and Airborne Radio System (SINCGARS) from ITT is undergoing upgrades to give the radio SDR capability.

Software and computers were key to the transition to software-defined radio. "Legacy radios were purpose-built RF devices that used RF frequencies. Computing technology was the natural evolution that turned radios into computers with RF front ends," says Kurt Grigg, director of marketing for communications products at Rockwell Collins. "It is a computer running this processing, or waveform, that enables networking and data sharing, with the RF front end transmitting and receiving the data. It has a lot of processing horsepower behind it."

Efforts, moreover, have been worth it. "We've come a long way," Tarver says. "We have demonstrated software-defined radios in the military and commercial sector, of taking a radio platform and programming it to do different protocols, or waveforms. The processing capabilities, versatility, and power of SDR have been demonstrated in real time."

Enabling technologies

Embedded computing is the primary enabling technology behind software-defined radio, and as embedded computing has evolved, so has SDR technology. Digital signal processing (DSP), field-programmable gate arrays (FPGAs), general-purpose processors, and software design and development tools all lend themselves to software-defined radio, and enable SDR technology to improve on roughly similar trajectories.

"To run our waveforms, our SDR technology has had to progress," says Rockwell Collins' Haag. "Our software-defined radios have become more capable and less power hungry, as the basic technology components became more powerful and cost-effective. We needed to host the software-defined part of the radio in a reasonable-sized package. Otherwise, our radios would be the size of refrigerators."

Rockwell Collins is giving the legacy AN/ARC-210 airborne radio SDR upgrades, which should add capability for Navy and Air Force combat aircraft.

Advances in software-design tools, automated software code generation, and real-time software compilers also have contributed greatly to the progress of SDR technology. "The way the software is developed has progressed a lot over the last 10 years," Haag says. "Efficient software is critical to run on smaller, yet more powerful microprocessors in software-defined radios."

The process of writing software today "takes longer than we would like," says Thales' Johnston. "There are tools to enable you to develop software quicker, and check for software defects. We have software development tools today to do automated testing of software, and that look for loops and software practices."

Also playing a big role in the evolution of software-defined radio is battery technology, Johnston points out. "Our batteries are about 1.5 inches by 3 inches by 3 inches, and we try to provide eight to 10 hours of mission life, of transmit/receive, per battery charge. We want chemistries that can provide more capacity in that size of package. We have gone from NiCad to nickel-metal-hydride to lithium-ion batteries, which now is the state of the practical art," Johnston continues. "We have moved from 4.8 amp-hour to 5.8 amp-hour capacities by changing the kinds of cells that are in the package."

The future of SDR

So where do we go from here? On the power side, future developments in fuel-cell technology undoubtedly will play a part in future software-defined radio. "The next step would be fuel cells and we might, in the next five years, see soldier-worn, fuel-cell systems in some sort of power pack that will power several items. Fuel cells embedded in the radios, however, might take until the 10-year time frame," Johnston says.

The sizes of software-defined radios also are expected to shrink on a similar path to embedded computing. "We are seeing the transition and evolution of the capabilities we have in our manpack radios down into the smaller-packaged radios and personal radios," says Harris' Turner. "Our AN/PRC-152A [soldier radio] now has wideband capability, and can do the kind of wideband networking that our manpack radio can do. As form factors shrink, we can get more and more capability in our radios, and that has really enabled our wideband capability."

In addition, military communications systems designers will consider embedding software-defined radio capability into other systems as SDR technology continues to become smaller in size, lighter in weight, and more stingy in power consumption. "We're already seeing a melding of technologies and capabilities," says Rockwell Collins' Grigg. "We could see wrist-mounted or helmet-mounted technology where the radio and display capability are merged."

Likewise, Rockwell Collins is upgrading its venerable AN/ARC-210 airborne radio with SDR technology—a process that should increase the radio's capability, and leave room in the chassis for far more functions than the radio can do today. "It is growing to become a networking software-defined radio. So, what is next?" Haag asks. "Now that I have a computer in my radio, I might find new ways of massaging the data."

New uses for software-defined radio are high on the U.S. Army's list of priorities, says General Dynamics' Tarver. "This is fairly new technology, and trying to understand how these networks will behave in terrain in the field is non-trivial," he says. "We're also looking at tying all the pieces together on the battlefield, and looking at command and control links for the robots, as well as for extracting sensor data. What better way would there be than for a soldier to access and extract that information to get a total picture of the battlefield?"

In addition, researchers are investigating embedding capability in software-defined radio sets to perform electronic warfare, signals intelligence, and even detecting chemical, biological, and radioactive agents on the battlefield, all without the radio user's involvement. "We now have to figure out the priorities and how we will use these systems," Tarver says.

Beyond SDR: cognitive radio

Looking beyond software-defined radio, experts say the next step is a smart, computer-controlled radio that in real time is able to sample the RF environment, locate vacant, interference-free frequencies, and establish communications links automatically. This concept is called cognitive radio, which should be even more computer-intensive than SDR, experts say.

"Cognitive radio is the next thing," says ITT's Whitehill. "It has intelligence to know what the right thing to do is, like listening to the environment and determining if frequencies are jammed, and to make use of other frequencies." Still, this kind of radio communications technology primarily will be in the future.

Handheld software-defined radio technology from Thales Communications can aid communications interoperability among U.S. and allied forces.

"It's a little before its time," says Rockwell Collins' Grigg. "We will see this exploited first in the commercial domain. In DOD, you deploy your radio systems with rigorous spectrum management. The concept of cognitive radio says if I have a congested spectrum, I can sense the spectrum, use areas of the spectrum in real time, and find a channel not being used. Today's tactics and logistics of the Army don't allow that.

Among the military challenges of cognitive radio are not simply finding unused frequencies, but determining how to rank each radio message or data transmission in importance, to find a way for the highest-priority radio and data traffic to get through first, and to enable lower-priority traffic to wait in line, he says.